Статья
11/18/2011

Enumerable.Sum<TSource> Method (IEnumerable<TSource>, Func<TSource, Nullable<Int32>>)

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Computes the sum of the sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence.

Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Sum(Of TSource) ( _
    source As IEnumerable(Of TSource), _
    selector As Func(Of TSource, Nullable(Of Integer)) _
) As Nullable(Of Integer)

public static Nullable<int> Sum<TSource>(
    this IEnumerable<TSource> source,
    Func<TSource, Nullable<int>> selector
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>
A sequence of values that are used to calculate a sum.

selector
Type: System.Func<TSource, Nullable<Int32>>
A transform function to apply to each element.

Return Value

Type: System.Nullable<Int32>
The sum of the projected values.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception	Condition
ArgumentNullException	source or selector is nulla null reference (Nothing in Visual Basic).
OverflowException	The sum is larger than MaxValue.

Remarks

This method returns zero if source contains no elements.

The result does not include values that are nulla null reference (Nothing in Visual Basic).

You can apply this method to a sequence of arbitrary values if you provide a function, selector, that projects the members of source into a numeric type, specifically Nullable<Int32> in C# or Nullable(Of Int32) in Visual Basic.

In Visual Basic query expression syntax, an Aggregate Into Sum() clause translates to an invocation of Sum.

Examples

The following code example demonstrates how to use Sum<TSource>(IEnumerable<TSource>, Func<TSource, Double>) to sum the projected values of a sequence.

Note:
This code example uses an overload of this overloaded method that is different from the specific overload that this topic describes. To extend the example to this topic, change the body of the selector function.

   Structure Package
      Public Company As String
      Public Weight As Double
   End Structure

   Sub SumEx1()
      ' Create a list of Package values.
      Dim packages As New List(Of Package)(New Package() _
           {New Package With {.Company = "Coho Vineyard", .Weight = 25.2}, _
            New Package With {.Company = "Lucerne Publishing", .Weight = 18.7}, _
            New Package With {.Company = "Wingtip Toys", .Weight = 6.0}, _
            New Package With {.Company = "Adventure Works", .Weight = 33.8}})

      ' Sum the values from each item's Weight property.
      Dim totalWeight As Double = packages.Sum(Function(pkg) _
                                                   pkg.Weight)

      ' Display the result.
      outputBlock.Text &= "The total weight of the packages is: " & totalWeight & VbCrLf
   End Sub

   ' This code produces the following output:
   '
   ' The total weight of the packages is: 83.7

      class Package
      {
         public string Company { get; set; }
         public double Weight { get; set; }
      }

      public static void SumEx1()
      {
         List<Package> packages =
             new List<Package> 
                     { new Package { Company = "Coho Vineyard", Weight = 25.2 },
                       new Package { Company = "Lucerne Publishing", Weight = 18.7 },
                       new Package { Company = "Wingtip Toys", Weight = 6.0 },
                       new Package { Company = "Adventure Works", Weight = 33.8 } };

         double totalWeight = packages.Sum(pkg => pkg.Weight);

         outputBlock.Text += String.Format("The total weight of the packages is: {0}", totalWeight) + "\n";
      }

      /*
       This code produces the following output:

       The total weight of the packages is: 83.7
      */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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